1. Field
One embodiment of the present invention relates to an apparatus (hereinafter referred to as “microphone-earphone”) which comprises a device for converting sound (acoustic signal) to an electric signal, is worn on the ear in use, and converts an electric signal to sound, and more particularly to a microphone-earphone configured to correct acoustic characteristics of the external auditory canal.
2. Description of the Related Art
Playback apparatuses, which enable listening of playback sound, such as music, with use of a headphone or an earphone, have being gaining in popularity. When music is listened to with use of a headphone or an earphone, there is such a case that the ear is closed by the headphone or earphone and a resonance phenomenon occurs, and the sound quality becomes unnatural due to the resonance phenomenon.
There has conventionally been proposed an earphone which includes a microphone-equipped earphone in order to achieve out-of-head sound image localization, wherein the acoustic characteristics of the external auditory canal are obtained by measurement using the microphone-equipped earphone, and a transfer function is found by using an adaptive equalization filter (Jpn. Pat. Appln. KOKAI Publication No. 2000-92589).
On the other hand, when music is listened to with the headphone or earphone, there is such a case that the playback sound deteriorates due to sound from the outside environment. In the prior art, there has been proposed a technique of noise cancellation for preventing deterioration of playback sound due to sound from the outside environment.
Jpn. Pat. Appln. KOKAI Publication No. H3-214893, for instance, discloses an earphone apparatus comprising an acoustic tube configured to have substantially the same inside diameter as the external auditory canal, and to have one end formed as an earlap decorative portion and the other end formed as a voice non-reflective end; an external microphone unit; an internal microphone unit; and a mixing circuit which can vary a mixture ratio between a signal obtained from the external microphone unit and a signal obtained from the internal microphone unit. The mixture ratio of the mixing circuit is varied, where necessary. Thereby, outside sound, etc. can be listened to, without removing the earphone apparatus from the ear, and noise from the outside is reduced (see Jpn. Pat. Appln. KOKAI Publication No. H3-214893).
In addition, Jpn. Pat. Appln. KOKAI Publication No. 2008-177798 discloses an earphone apparatus for exactly measuring the acoustic characteristics of the external auditory canal, with the earphone apparatus being worn on the ear. The earphone apparatus is put on a part of the listener's earlap, and a sound image is output from a moving-coil type sound source, which is provided in the housing, toward the listener's eardrum. A second sound source, apart from a first sound source, is provided in the housing.
In the technique disclosed in the above-described KOKAI No. 2000-92589, however, if the microphone is disposed between the speaker of the earphone and the external auditory canal, the sound output from the speaker is blocked by the microphone, and the playback sound is degraded. In some cases, when the acoustic characteristics of the external auditory canal are obtained, a signal output from the speaker is disadvantageously acquired.
In the above-described KOKAI No. 2008-177798, in order to advance the technique in KOKAI No. 2000-92589, the second sound source is used as a sound source for measurement, and the first sound source is used as a microphone. In this technique, however, it is necessary to use the second sound source that is limited to the use for measurement, and it is difficult to provide the commodity value commensurate with the increase in system cost. Besides, depending on the kind of sound that is used for measurement, since the first sound source is disposed in front of the second sound source, the measured sound is blocked and the exact characteristics are hardly measured.